Manufacture of metal sheet or strip



Aug. 21, 1962 w. K. J. PEARSON MANUFACTURE OF METAL SHEET OR STRIP 3Sheets-Sheet 1 Filed Sept. 15, 1958 FIGI Vol/age Reference TachoGenera/5r Aug- 21, 19 w. K. J. PEARSON MANUFACTURE OF METAL SHEET ORSTRIP 3 Sheets-Sheet 2 Filed Sept. 15, 1958 Aug. 21, 1962 w. K. J.PEARSON 3,049,950

MANUFACTURE OF METAL SHEET OR STRIP Filed Sept. 15, 1958 3 Sheets-Sheet3 FIGS {3 36 57 E- I 9 13 United States Patent 3,049,950 MANUFACTURE OFMETAL SHEET OR STRH William Kenneth .Iamieson Pearson, Denham, England,assignor to The British Aluminium Company Limited, London, England, acompany of Great Britain Filed Sept. 15, 1958, Ser. No. 761,231 Claims.(Cl. 56)

The term flatness" refers to the surface of the sheet.

or strip produced and the term, shape refers to the cross-sectionalshape of the sheet or strip. Sheet or strip may be considered to be ofgood shape when it does not possess a double curvature. Usually thecross-sectional shape is uniform throughout the length of the sheet orstrip but the sheet or strip may taper along its length whilst stillbeing of good shape. I g

In the manufacture of metal sheet or strip by pass ing the materialthrough a pair of co-operating rolls in a rolling mill it is usual toprovide at least one of the rolls with a cambered surface, initially byappropriately grinding the roll and additionally by superposing athermal camber thereon, in order to compensate for deflections of therolls due to the separating force exerted by the rolled material. Thuseach cambered roll has a surface which. is curvilinear in a planecontaining the roll-axis, is circular in a plane transverse to therollaxis, is symmetrical about a transverse plane passing through thecentre of length of the r'ollaxis and has its greatest diameter in thelast-mentioned plane when at its working temperature. During the rollingoperation the thermal camber of the cambered roll surface is controlledby controlling the temperature gradient existing in the roll in adirection parallel to its axis. In the operation of the rolling mill theflatness or shape of the sheet or strip entering the bite of theco-operating rolls is retained or improved as required according to theshape of the surfaces of the rolls at the bite and this shape dependsupon the initial shape of the surfaces of the co-operating rolls and thereactionary forces exerted on these surfaces at the bite by the materialto deform these surfaces. These reactionary forces in turn depend uponthe screw-down force applied to urge the rolls towards each other, thefriction influenced by lubrication of the roll surface and the tension(if any) applied 3,49,950 Patented Aug. 21, 1962 highly skilledoperators to assess the flatness or shape and take the correct remedialaction.

Variation in the roll camber can be corrected by suitably controllingthe temperature gradient across the roll or it can be compensated for bymodifying the screwdown force and/or the tension (if any) in thesheet;or strip.

It is an object of the present invention to providean improved methodand apparatus for controlling theflatness or shape of metal sheet orstrip produced in a rolling mill.

to the sheet or strip. The roll surface friction is usuallysubstantially constant during the rolling operation and is difficult tovary during such operation. The remaining factors, namely the rollshape, the screw-down force and the sheet or strip tension (if any) arecapable of being varied during a rolling operation and are hereinafterreferred to as the controlling factors.

During the rolling operation the camber of the rolls tends to change dueto fluctuations in the temperature gradients across the rolls and it hashitherto been diflicult to control or compensate for this effect owingto the lack of a precise and continuous method of and means formeasuring it. This variation in the camber of the rolls has resulted inundesirable variations in the flatness or shape of the sheet or stripproduced. This defeet is particularly undesirable in strip materialwhich is too long to be corrected by subsequent flattening operations.Hitherto it has been customary to assess the flatness or shape of thesheet or strip by visual inspection and the use of tension on the sheetor strip and high rolling speeds has made it increasingly diflicult evenfor According to one feature of the present invention a method ofcontrolling the flatness or shape of metal sheet or strip produced bypassing the material through the bite of a pair of co-operating rolls ina rolling mill comprises measuring the difference between the radii ofat least one of the rolls at at least two axiallyspaced locations, andmodifying at least one of the controlling factors in ac: cordancewiththe magnitude of the departure of said difference from apredetermined value in the sense to correct or compensate for suchdeparture.

Preferably the difference between the roll radii is measured bymeasuring the' linear velocity of the surface of the roll at saidlocations and this is conveniently done by applying aroller in non-slipfrictional engagement with the roll at each "such location and measuringthe angular velocity imparted to each such roller, the rollersadvantageously having. their axes contained in a common plane containingthe roll axis, and one roller being disposed substantially centrally ofthe length of the roll.

Accordingfto. another feature of the invention apparatus for carryinginto effect the method according to either of the two immediatelypreceding paragraphs comprises means for measuring the differencebetween the radii of at least one of the rolls at at least two axiallyspaced locations and means responsive to such difference to provide anoutput signal having a magnitude which is a function of the departure ofsaid difference from a predetermined value.

Preferably the measuring means comprises a roller applied in non-slipfrictional engagement with the roll at each such location.

Advantageously means is provided responsive to said output signalautomatically to modify at least one of the controlling factors in thesense referred to.

In order that the invention may be more clearly understood an examplethereof will now be described with reference to the accompanyingdrawings in which:

FIG. 1 is an elevational view of a roll for use in a rolling mill andhaving a camber which is exaggerated for the purpose of clarity;

FIG. 2 is a somewhat diagrammatic elevational view of a strip rollingmill;

FIG. 3 is a section taken on the line IIIIII of FIG. 2; 1

FIG. 4 is a block circuit diagram, and

FIG. 5 is a circuit diagram showing in greater detail a circuit similarto FIG. 4.

The roll 1 illustrated in FIG. 1 is shown with an exaggerated camber andit will be seen that it is substantially barrel-shaped, ire. the roll 1has a surface which is curvilinear in a plane containing the roll-axis,is circular in a plane transverse to the roll-axis, is symmetrical abouta transverse plane passing through the centre of length of the roll-axisand has its greater diameter in the lastmentioned plane when at itsworking temperature. In practice the camber is very slight and isusually formed by grinding the roll which may be ground initially toconvex shape or it may be ground initially flat or concave to allow forthermal expansion during the rolling operation. Two-such cambered rolls1 are provided in shaft 2 of the lower roll 1 is carried in fixedbearings (not shown) and. the shaft 2 of the upper roll 1 ismovabletowards the lower roll by means of screwdown members 4 whereby the forceurging/the rolls 1 together is controlled. 1 I

This example is concerned with the manufacture of metal strip and theprimary material indicated at 5 (FIG. 3) is fed to the bite of the rollsand emerges'therefrom "as the final strip 6. As will be appreciated theprimary material 5 may have been pre-rolled to a. predeterminedthickness. The strip 6 is taken up on a positively driven roller 7carried on a shaft 8 whereby tension is imparted to the strip 6. Twomeasuring rollers 9 are arranged to bear on the upper roll 1 in non-slipfrictional contact so as to be driven thereby, the axes of these rollers9 being contained in a common plane containing the axis of the upperroll 1. The rollers 9 are preferably of equal diameters as shown,although they need not necessarily be so and one is disposedsubstantially centrally of the width of the upper roll 1 and the otheris disposed between the centrally disposed roller 9 and one end of theroll. j

I The angular velocity imparted to each roller 9 by: the

upper roll 1 is proportional to the'linear' velocity of that part of thesurface driving it andhence is proportional-to the radius of the roll atthat location. It will be seen therefore that'the dilierence hr theangular velocities imparted to'the rollers 9 is a measure of thedifference between the radii of the'roll 1 to which they are applied atthe locations at which they are applied, and any departure of thisdifference from a predetermined value may be utilized to modify at.least one of the controlling factors, ie the roll camber, the striptension or the screw-down force exerted on the rolls 1 ,by the screwdownmember or members 4.. V

In this example the camber of the, upper roll 1 is controlled by meansof an oilpipe 10 feeding pipes 10a, ltib and Ida extending parallel tothe axis of the roll 1 by way of branch pipes 10d, 10c and 10respectively. The pipes 10a, 10b and 100 are provided with a'number ofspraying apertures 11 along their length through which oil is sprayed onto the surface of the r0111 on that part thereof advancing towardsthebite of the rolls. The pipe 1% is disposed between the pipes 10a and19c so that the oil therefrom controls the temperature of the mid-partof the surface of the roll 1 parallel to its axis and the oil from thepipes 10a and 100 controls the temperature of the surface of the roll1=along its marginal edges. A manually adjustable valve 11a controls theoil flow to the pipe 10 and an automatically controlled valve 111;controls the flow of oil to the pipe 10b thereby controlling the flow ofoil from the latter relative to the oil fiow from the pipes 10a and 100.After the surface of the upper roll 1 has passed the bite, any oilremaining thereon together with dirt and metal slivers is wipedtherefrom by a wiper 110. Thus by suitably controlling the valve 11b theoil flow from thespraying apertures 11 of the pipe 102': may becont-rolled and hence the temperature gradient and the roll camber andstrip shape may be controlled. This control may be exercised. by anoperator observing the d-ilference in the angular velocities imparted tothe rollers 9 or automatically in accordance with such dilference.

The block schematic circuit diagram of FIG. 4 shows an apparatus forautomatically utilizing the diiference in the angular velocitiesimparted to the rollers 9.

One of the rollers 9 drives a synchro transmitter 12 through a gear 13and the other roller 9 drives a synchro differential transmitter 14through a gear 15, the electrical output from the synchro differentialtransmitter 14 being a three phase electrical signal with electricalrotation at the difference speed which is fed to a synchro controltransformer 16. The latter is a comparison I camber 0f the rolls.

element in a servo loop which causes the rotor of the transformer 16 totrack the electrical rotation and the mechanism of the servo loopoperates as a torque amplifier which produces an output of sufficientmagnitude to be utilized to exercise the desired control. The servoloo-p comprises a demodulator 17, a DC. amplifier 18 and a servo-motor19 the output from which drives the highspeed end of a gear 20 thelow-speed end of which drives the control transformer-16 to provide amechanical monitoring feed-back. Stabilizing feed-back is provided by atachogenerator 21 mechanically coupled to the servo-motor 19. Thistachogenerator 21 provides an output which is an integral function ofthe output from the differential transmitter 14 and hence provides avoltage analogue of the difierence between the angular velocitiesimparted to the rollers 9, and this output is amplified by amplifier 22and utilized to provide a visual indication .at 23 of the differencebetween the angular velocities for manual control purposes.

To correct for the influence of changing mill speeds, a secondtachogenerator 24 is coupled to the mill-motor, mill rolls 1 or thestrip 6 (indicated generally by the reference .25) to provide a voltageanalogue of the rolling speed. This voltage analogue is subtracted froma fixed reference voltage provided at 26 in an amplifier 27 to producean output from the latter which is inversely proportional to the rollingspeed and which is utilized to energise the field of the tachogenerator21. In this way the output of the tachogenerator 21 and the indicationat 23 is a linear function of the quotient of the difierence between theangular velocities imparted to the rollers 9 and the rolling speed andhence is a measure. of the An interlocking stabilizing feedbacksignalmay be provided by feeding the amplified output of thetachogenerator 21 through a stabilizing network 29 to the amplifier 18.

The output from the tachogenerator 21 is compared in the amplifier 22with a predetermined reference value supplied as a voltage from 22A,which latter bears the legend Setting Camber or Shape in FIG. 4. Thispredetermined value supplied by 22A corresponds. to the desired camberof the rolls 1and the resultant output from the amplifier 22 is fed to afinal controlling element 28 which controls at least one of thecontrolling factors, which in this example is the camberof the rolls 1by controlling the valve 11b and hence the oil supply through thespraying apertures 11 of the pipe 10b, in the sense to reduce thedifference between the angular Velocities imparted to the rollers 9.

It 'will be appreciated that the output signal may be used to controlthe drive of a motor to the spindle 8 to control the strip tension or tocontrol a screw-down motor connected to the members 4 to control thescrewdown force.

It will be appreciated'that the rollers 9 need not necessarily be of thesame diameter in which case the difference between the angularvelocities imparted to them will have to be compared with a referencevalue to obtain a signal useful for control purposes.

It will be further appreciated that if sufiiciently accurate speedmeasuring elements are available they may be used in place of thesynchros 12 and 14 to give a difference voltage which. could be feddirectly to the amplifier 22, a computing element being provided todivide this signal by a voltage analogue of the mill speed and the units16, 17, 18, 19, 20, 21, 26 and 27 being no longer required.

FIG. 5 illustrates an electric circuit similar to that of FIG. 4 but ingreater detail. In this example one roller 9 drives through gear 13 therotatable winding 30 of a synchro transmitter 31 the fixed winding 32 ofwhich is electrically connected to the rotatable winding 33 of a synchrodifferential transmitter 34. The rotatable winding 30 is connectedacross terminals 35 to a source of AC. supply. The other roller 9 drivesthrough gear 15 the rotatable winding 36 of a synchro differentialtransmitter 37 the fixed winding 38 of which is electrically connectedto the fixed winding 39 of the transmitter 34. The fixed windings 4t)and 41 of synchro control transformers 42 and 43 respectively areconnected in parallel across the rotatable winding 36. The respectiverotatable windings 44 and 4-5 of the transformers 42 and 43 have theiroutputs respectively supplied across the fixed pairs of terminals 46 and47 of a double-pole switch 48 the movable pair of contacts of which maybe switched to take the output from either one of the rotatable windings44 and 45 and apply it across a pre-set sensitivity resistor 49 to feeda phase-sensitive rectifier 50. The rotatable windings 44 and 45 arerespectively geared through ratios of :1 and 100:1 to a shaft 51 gearedthrough a ratio of 100:1 to a split-field motor 52 the armature 53 ofwhich is connected across terminals 54 to a DC. supply. The fieldwinding 55 of the motor 52 is connected to the output of a DC. amplifier56 the input of which is connected to the output of the phase-sensitiverectifier 50. The motor 52 also drives a tachogencrator 57 having anoutput applied across a feed-back resistor 58 connected to the inputside of the phase-sensitive rectifier St). The motor 52 also drives asquare-law D.C. tachogenerator 59 through gearing 60, the tachogenerator59 having a separately excited field and being capable of being used formultiplication. One winding 61 of the tachogenerator is connected inseries with a linear wire-wound potentiometer resistor 62 of about 4Kacross terminals 63 connected to a D.C.

' supply of about 25 volts, the movable tapping 64 being connected tothe one end of the resistor 62 connected directly to one of theterminals 63. The position of the tapping 64 therefore controls themagnitude of the field produced by the winding 61 and the output of thetachogenerator 59 produced in armature winding 65 is a function of theproduct of this field and the speed of rotation of the tachogenerator 59driven by the gearing 60.

A roller 66 bearing upon the metal strip is driven at a speed which is afunction of the speed of advance of the strip and drives through gearing67 having a ratio of about 3:1 a permanent magnet tachogenerator 68 soas to produce an output of about 80 volts from the latter at a stripspeed of 800 feet per minute. This output is applied across a 100Klinear wire-wound potentiometer 69.- The potentiometer 69 has a limitstop 70 at 10K from the high voltage end and the tapping 71 is connected to a source 72 of a reference voltage which is applied across thetapping 71 and the high voltage end of the potentiometer 69 and theinput of an amplifier 73 the output of which is supplied to a motor74which drives both tappings 64 and 71 which are mechanically linked. Theoutput of the winding 65 of the tachogenerator 59 is applied through aresistor 75 to the input of an amplifier 76 the output of which is fedboth to an indicator 77 and an actuator 78 for the valve 11b. The outputof the amplifier 76 is connected to the input of the latter through afeedback resistor 79 and is also connected to a biased relay 8%connected through an amplifier 81 to a motor 82 connected to therotatable winding 33 of the synchro differential transmitter 34. Themotor 82 also drives a tachogenerator 83 the output of which is fed backto the input of the amplifier 81 to provide a stabilizing loop. Areference voltage is supplied to the input of the amplifier 76 from asource 84 connected thereto through resistor 85.

The operation of this circuit will now be described. For the purpose ofthis description the fixed winding 32 of the synchro transmitter 31 maybe considered to be connected directly across the fixed winding 38 ofthe synchro differential transmitter 37. It will be apparent that inthis case the rotating fields produced in the fixed windings 40 and 41of the transformers 42 and 43 is a function of difference in thevelocity of rotation of the 6. rollers 9 and the rotation of thewindings 44 and 45 thereof will be a similar function. The movablecontact of the switch 48 is connected across the terminals 46 or 47 toselect the output either from the rotatable windings 44 or the winding45 respectively driven by the motor 52 through permanently meshedgearing of 1000z1 and 10,0801. The motor 52, phase-sensitive detector5%) and amplifier 56 provided with stabilising feedback fromtachogenerator '52 track either trans-former 42 or. 43 according to thespeed ratio selected and hence enable the apparatus to be made effectiveover a wide range of speed difference of the rollers 9. The motor 52drives the tachogenerator 57 and hence the square-law tachogener-ator 59at a speed which is a linear function of the velocity difference of therollers 9. The permanent magnet generator 68 provides an output which isan integrated function of the speed of advance of the strip measured bythe roller 66 and this is inverted by the self-balancing potentiometersystem 62, 69 and applied across the winding 61 of the square-lawtachogenerator 59. The latter integrates the velocity difference signalfrom the rollers 9 and provides an output which is the product of thisintegral and the reciprocal of the integral of the velocity of thestrip. This product is the desired signal and is compared in theamplifier 76 with the reference voltage from the source 84 to producethe desired indication in the indicator 77 and the appropriate operationof the valve 1112 due to the actuator 78. In practice thereferencevoltage of the source 84 will usually be zero when the rollers 9 are ofequal r'adii but it may be set up initially to a predetermined valuewhere the rollers 9 are not of equal radii or adjusted from time to timeto compensate for changes in the radii of therollers 9 due to wear andcan also be used to compensate for drift in the amplifier 56 althoughthis could be better dealt with by providing a separate zero check. Thesource 84 may also be set up initially to a predetermined value when agiven deviation from flatness is desired.

The synchro difierential transmitter 34 and the connections thereto, themotor 82, tachogenerator 83, amplifier 81 and relay 8% are provided toensure a rapid electrical line-up of the rotating fields of thetransmitters 31 and 37. Thus should transmitters 31 and 37 get out ofphase when the apparatus is started up, the amplifier 76 will saturateand operate the relay 8t and cause the motor 82 to drive the rotatablewinding 33 to bring the rotating fields into synchronism in a matter ofseconds. When synchronism is nearly achieved the relay 80 opens and themotor 32. ceases to function.

It will be understood that where a number of pairs of rolls 1 areprovided in series in a tandem rolling mill the signal derived from apair of rollers 9 bearing on a roll 1 of a pair of such rolls may beutilised to modify at least one of the controlling factors relating to apreceding or succeeding pair of rolls 1 in the series so as to ensurethat the stripfinally emerging from the mill shall have the 1 desiredflatness or shape.

It will be further understood that more than two rollers 9 may beprovided across the roll 1 and switch means may be provided successivelyto compare the angular velocities imparted to pairs of such rollers or apair of rollers may be traversed axially along roll 1 in order to seekcamber irregularities.

When sheet is being rolled it is usually not placed under tension and insuch a case the signal derived from the angular velocities imparted tothe rollers 9 is utilized to modify the screw-down force applied to therolls 1 and/ or the camber of the roll or rolls 1.

It will be understood that the invention is applicable to controllingthe shape of profiled sheet or strip material.

What I claim is:

l. A method of controlling the flatness or shape of metal strip producedby passing the strip through the bite of a pair of cooperating rolls ina rolling mill, which includes the following steps: measuring thedifference becontrolling factor that is contributing to any departure inthe difference between said radii from said predetermined differencevalue in accordance with the magnitude of such departure from thepredetermined difference value in order to correct and compensate forsuch departure and restore the difference between said radii to adifference corresponding to said predetermined difference value.

2. A method according to claim 1, which includes the step of measuringthe difference between said roll radii by measuring the linear velocityof the surface of the roll at each of said axially spaced locationsthereon.

3. A method according to claim 1, which includes the step of measuringthe linear velocity of the surface of the roll at said two axiallyspaced locations, respectively, by measuring the angular velocity of aroller in non-slip frictional engagement with the roll at each suchlocation.

4. A method according to claim 1, which includes the steps of derivingan electrical signal from rollers in nonslip frictional engagement withone of said rolls at said axially spaced locations thereon,respectively, which electrical signal is a function of the rollingspeed; and then producing from said electrical signal a control signalwhich is a function of the product of the difference of the angularvelocities imparted to the rollers and the reciprocal of said rollingspeed electrical signal;

5. A method of controlling the flatness or shape of metal strip producedby passing the strip through the bite.

of a p'air of cooperating rolls in a rolling mill, which includes thesteps of: measuring the difference between the radii of at least one ofsaid rolls at at least two axially spaced locations along the roll;establishing a predetermined difference value between said radii;measuring any difference between said radii of said roll at such spacedlocations against said predetermined difference value; and

then modifying the shape of one of said rolls in accordance with themagnitude of the departure of any difference between said radii fromsaid predetermined difference value to correct and compensate for suchdeparture and restore the difference between said radii to a differencecorresponding to said predetermined difference value.

6. In a rolling mill, in combination, a pair of cooperating rolls forpassing through the bite thereof a metal strip; means for measuring thedifference between the radii of at least one of said rolls at at leasttwo axially spaced locations along said roll; means for establishing apredetermined difference value between said radii; means for measuringany difference between said radii against said predetermined differencevalue; and means responsive to difierences in said radii providing anoutput signal having a magnitude which is a function of the extent ofany such departure from said predetermined difference value.

7. In a rolling mill, in combination, a. pair of cooperating rolls forpassing a metal strip through the bite thereof; means for measuring thedifference between the radii of at least one of said rolls at at leasttwo axially spaced locations therealong; means for establishing apredetermined difference value between said radii; means for measuringthe difference between said radii against said predeterjmined differencevalue; means responsive to differences in said radii to provide anoutput signal which is a function of the magnitude of the departure ofany such difference from said predetermined difference value; and meansresponsive to said signal to automatically modify a controlling factorcontributing to a departure from said predetermined difference value tocorrect and compensate for such departure and restore the differencebetween said radii to one corresponding to saidpredetermined differencevalue. a

8. In a rolling mill, in combination, a pair of cooperating rolls forpassing through the bite thereof a metal strip;- means for modifying theshape of at least one of said pair of cooperating rolls; measuring meansfor measuring the difference between the radii of at least one of saidrolls at at leasttwo axially spaced locations therealong; means forestablishing a predetermined difference value between said radii;difference measuring means formeasuring the difference between saidradii against said predetermined difference value; means responsive todifferences in said radii providing an output signal which is a functionof the magnitude of the departure of any such difference from saidpredetermined difference value; and means responsive to said signal toautomatically effect operation of said means for modifying the shape ofone of said rolls to correct and compensate for such departure andautomatically restore the difference between said radii to onecorresponding to said predetermined difference value; I

9. In a rolling mill, in combination, a pair of cooperating rolls forpassing through the bite thereof a meta-l strip; means for applying ascrew-down force to said rolls urging said rolls radially toward eachother to engage the strip between the bite of said rolls; measuringmeans for measuring the difference between the radii of at least one ofsaid rolls at at least two axially spaced locations therealong; meansestablishing a predetermined difference value between saidradii;.difference measuring means for measuring the difference betweensaid radii against said predetermined difference value; means responsiveto differences in said radii to provide an output signal which is afunction of the magnitude of the departure of any such difference fromsaid predetermined difference value; and means responsive to said signalto automatically effect operation of said means for applying ascrew-down force .to said rolls to correct and compensate for suchdeparture and restore the difference between said radii to onecorresponding to said predetermined difierence value.

10. In a rolling mill, in combination, a pair of cooperating rolls forpassing through the bite thereof a metal strip; means for applyingtension to the metal strip in the direction of its advancement from thebite of said rolls; measuring means for measuring the difference betweenthe radii of at least one of said rolls at at least two axially spacedlocations therealong; means for establishing a predetermined differencevalue between said radii; difference measuring means for measuring thedifference between said radii against said predetermined differencevalue; means responsive to differences in said radii to provide anoutput signal which is a function of the magnitude of the departure ofany such difference from said predetermined difference value; and meansresponsive to said signal to automatically effect operation of saidmeans for applying tension to said strip to modify the tension appliedthereby to correct and compensate for such departure and restore thedifference between said radii to one corresponding to said predetermineddifference value.

References (lit-ed in the file of this patent UNITED STATES PATENTS2,292,535 MacChesney Aug. 11, 1942 2,811,059 Appleby Oct. 20, 19572,851,911 Hessenberg Sept. 16, 1958

